#include "sched.h"

/*
 * stop-task scheduling class.
 *
 * The stop task is the highest priority task in the system, it preempts
 * everything and will be preempted by nothing.
 *
 * See kernel/stop_machine.c
 */

#ifdef CONFIG_SMP
static int
select_task_rq_stop(struct task_struct *p, int cpu, int sd_flag, int flags)
{
    return task_cpu(p); /* stop tasks as never migrate */
}
#endif /* CONFIG_SMP */

static void
check_preempt_curr_stop(struct rq *rq, struct task_struct *p, int flags)
{
    /* we're never preempted */
}

static struct task_struct *
pick_next_task_stop(struct rq *rq, struct task_struct *prev, struct pin_cookie cookie)
{
    struct task_struct *stop = rq->stop;

    if (!stop || !task_on_rq_queued(stop))
        return NULL;

    put_prev_task(rq, prev);

    stop->se.exec_start = rq_clock_task(rq);

    return stop;
}

static void
enqueue_task_stop(struct rq *rq, struct task_struct *p, int flags)
{
    add_nr_running(rq, 1);
}

static void
dequeue_task_stop(struct rq *rq, struct task_struct *p, int flags)
{
    sub_nr_running(rq, 1);
}

static void yield_task_stop(struct rq *rq)
{
    BUG(); /* the stop task should never yield, its pointless. */
}

static void put_prev_task_stop(struct rq *rq, struct task_struct *prev)
{
    struct task_struct *curr = rq->curr;
    u64 delta_exec;

    delta_exec = rq_clock_task(rq) - curr->se.exec_start;
    if (unlikely((s64)delta_exec < 0))
        delta_exec = 0;

    schedstat_set(curr->se.statistics.exec_max,
            max(curr->se.statistics.exec_max, delta_exec));

    curr->se.sum_exec_runtime += delta_exec;
    account_group_exec_runtime(curr, delta_exec);

    curr->se.exec_start = rq_clock_task(rq);
    cpuacct_charge(curr, delta_exec);
}

static void task_tick_stop(struct rq *rq, struct task_struct *curr, int queued)
{
}

static void set_curr_task_stop(struct rq *rq)
{
    struct task_struct *stop = rq->stop;

    stop->se.exec_start = rq_clock_task(rq);
}

static void switched_to_stop(struct rq *rq, struct task_struct *p)
{
    BUG(); /* its impossible to change to this class */
}

static void
prio_changed_stop(struct rq *rq, struct task_struct *p, int oldprio)
{
    BUG(); /* how!?, what priority? */
}

static unsigned int
get_rr_interval_stop(struct rq *rq, struct task_struct *task)
{
    return 0;
}

static void update_curr_stop(struct rq *rq)
{
}

/*
 * Simple, special scheduling class for the per-CPU stop tasks:
 */
const struct sched_class stop_sched_class = {
    .next           = &dl_sched_class,

    .enqueue_task       = enqueue_task_stop,
    .dequeue_task       = dequeue_task_stop,
    .yield_task         = yield_task_stop,

    .check_preempt_curr     = check_preempt_curr_stop,

    .pick_next_task     = pick_next_task_stop,
    .put_prev_task      = put_prev_task_stop,

#ifdef CONFIG_SMP
    .select_task_rq     = select_task_rq_stop,
    .set_cpus_allowed       = set_cpus_allowed_common,
#endif

    .set_curr_task      = set_curr_task_stop,
    .task_tick          = task_tick_stop,

    .get_rr_interval    = get_rr_interval_stop,

    .prio_changed       = prio_changed_stop,
    .switched_to        = switched_to_stop,
    .update_curr        = update_curr_stop,
};
